The present invention relates to a warming device for a fuel cell system having a fuel battery and a power storage device.
In recent years, attention is being given to fuel cells, which are clean and provide high energy efficiency, as power sources for electric vehicles. A fuel battery produces an electromotive force by a chemical reaction of oxygen with hydrogen. Oxygen is supplied to a cathode, and hydrogen is supplied to an anode, and chemical energy obtained by the reaction of oxygen with hydrogen is directly converted into electric energy, thus providing high conversion efficiency.
For use in a fuel cell vehicle, a compact fuel battery with high output is required, and a polymer electrolyte fuel cell (PEFC) is preferably used. The polymer electrolyte fuel cell efficiently generates electric power at a preset temperature (about 80° C.). Since a reaction that produces heat occurs in the fuel battery, efficient power generation can be continued even at a low ambient temperature after a lapse of predetermined time from a start of power generation. However, if the temperature is low (for example, 0° C. or less) at the start of the power generation, power cannot be generated or is inefficiently generated.
Water generated in the fuel battery is generally discharged together with unreacted gas. However, generated water sometimes remains in a gas passage when the fuel battery is stopped. If an outside air temperature is 0° C. or less, which is a freezing point of water, in a cold district, water remaining in the gas passage may freeze to block the gas passage, thus preventing flow of fuel gas. This prevents the fuel battery from being activated.
At a low temperature, moisture in an electrolyte membrane of the polymer electrolyte fuel cell may freeze, which may prevent power generation or significantly reduce power generation efficiency. Even at a temperature that causes no freeze of water, the polymer electrolyte fuel cell generally generates power at the preset temperature, and thus requires quick warming on a cold day.
For example, Japanese Laid-Open Patent Publication No. 63-91967 discloses a method for heating a fuel battery main body and a storage battery in a power supply device including a fuel battery and the storage battery in combination, by detecting a temperature in a housing container in which the fuel battery main body and the storage battery are placed, and energizing a heater for heating the inside of the housing container from the storage battery when the detected temperature is below a set value. The Laid-Open Japanese Patent Publication No. 63-91967 also discloses a method for energizing a heater for heating the fuel battery when the temperature in the housing container is between −15° C. and −5° C., inclusive, and energizing a heater for heating the fuel battery and a heater for heating the storage battery when the temperature in the housing container is −15° C. or less.
For example, Japanese Laid-Open Patent Publication No. 3-272567 discloses a hybrid fuel battery in which a fuel battery and a storage battery are combined and connected to the same load, and a temperature of the storage battery is kept within a predetermined range in order to prevent reduction in capacity of the storage battery at a low temperature. The hybrid fuel battery includes a temperature sensor provided in the storage battery for detecting the temperature of the storage battery, a heating device for heating by remaining heat or electricity generated by the fuel battery, and a control part that controls the heating device so as to keep the temperature of the storage battery within the predetermined range based on the temperature detected by the temperature sensor.
As a warming method of a fuel battery, for example, Japanese Laid-Open Patent Publication No. 2002-93445 discloses a method in which a temperature detection device for detecting a temperature of the fuel battery, and an air heating device for heating air to be supplied to an air electrode of a fuel cell are provided, and the air heating device is actuated when the temperature of the fuel cell is a preset temperature or less. The air heating device includes a heater to which power is supplied from a storage battery.
In the method disclosed in Japanese Laid-Open Patent Publication No. 63-91967, the fuel battery and the storage battery (secondary battery) are heated by the heater actuated (driven) by the power from the storage battery, and the heater is actuated without the storage battery being preheated. However, a secondary battery incorporated in a fuel cell vehicle produces high output at a normal temperature (a temperature that requires no warming), but remains producing low output at a low temperature that requires warming. Therefore, if the method described in Japanese Laid-Open Patent Publication No. 63-91967 is applied to warming of a fuel cell vehicle, the heater is energized in a low output state of the secondary battery to warm the fuel battery and the secondary battery, which takes much time.
In the hybrid fuel battery disclosed in Japanese Laid-Open Patent Publication No. 3-272567, the heating device is controlled to detect the temperature of the storage battery by the temperature sensor and keep the temperature of the storage battery within the predetermined range. However, the heating device is heated by the remaining heat or the electricity generated by the fuel battery, which requires the fuel battery being always actuated. Therefore, when the hybrid fuel battery is applied to the case where warming is required at a low temperature such as the case of a fuel cell vehicle used in a cold area, power generation by the fuel battery for warming is required even during the fuel cell vehicle being not used.
In the warming method described in Japanese Laid-Open Patent Publication No. 2002-93445, the fuel cell is heated by the heater to which the power is supplied from the storage battery when the temperature of the fuel cell is the preset temperature or less. In this case, no consideration is given to low output of the storage battery at a low temperature, and warming takes much time as in Japanese Laid-Open Patent Publication No. 63-91967.